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"Bypass caps" and their effect on perceived sound

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Sorry, couldn't resist.
The capacitance value needed for desired ripple rejection in a given circuit is not really open for debate.
As for sound quality, everything is open...

/Olof

Good point, but I assume these values will be exceeded anyway...

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Good film caps are pricey, and using all film for the PS definitely raises the cost quite a bit, PS caps and coupling caps are probably 25% of the total parts cost of my amp, but the differences in ESR are an order of magnitude or so and this is clearly audible. Also, some high frequency harshness is gone by getting rid of the electrolytic. Unfortunately, electrolytics poison the sound of an amplifier, especially in the signal path and final stage of the PS.
 
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Unfortunately, electrolytics poison the sound of an amplifier, especially in the signal path and final stage of the PS.

Electrolytics particularly poison the sound as cathode bypasses. I spent a whole afternoon clipping and unclipping about a dozen caps as cathode bypasses. The electrolytics were horrible, bypassed or not. Even the film caps added some fog to the sound. I now use filament bias to eliminate caps altogether in the cathode circuit. And I also couple stages with interstage transformers to avoid coupling caps. Basically I'd always take iron over a cap, even a teflon one and the rest are worse. There's a whole boutique capacitor culture out there and a lot of money is spent, but where there's the option of not using a cap at all, I think that's the route to take. Otherwise film caps everywhere in the PSU where you can't avoid them.
 
You tube guys are funny.
Some of us use JFETs, MOSFETs and SITs and have .4 Farad power supplies. Think about an all film supply? Naw!
I have been through the gamut with tubes in all stages, preamps, power amps, triodes, tetrodes, pentodes, choke loaded, transformer coupled and right now I am enjoying Nelson Pass' F5 and F5T, F6, Salas Simplistic Phono, DCB1, etc.
Back to by passing electrolytic power supply caps with film.

Rush
 
It's funny how these conversations can wander...

The original question was about power supply capacitors, where electrolytics are often unavoidable, especially in power amps that draw too much current for most regulated supplies.

I agree that you can hear an electrolytic cap used as a bypass on a cathode resistor. I've tested that for myself, and I'll usually resort to either leaving the cathode resistor unbypassed (and accepting the changes in performance), or using an LED or two to make the bias voltage.

But in a power amp main power supply, I'll often need something like +470V at 200mA, and let's say that's in a Dyna ST70 chassis (cramped). There's nowhere near enough room to fit a couple of 47uF 630V Solen caps, motor run PPIO caps, or something like that. So high-voltage electrolytics will need to be used.

--
 
IMO, Wavebourn offers wise advice to always think about current flow. You need to think about the design in terms of both LF and RF. Zero impedance is not always a good thing, as it's easy to get ringing against circuit inductance. If you're trying to kill off RF, you have to do it at the source, which is usually the rectifiers.

Getting a very low impedance across a wide band is difficult. It can't be done by bypassing electrolytics with the usual values of film caps. Using motor run or similar large films will do it. The math is a PITA and making decent measurements on the bench is more difficult than one might think, but it can be proven with the right gear. Plots from a wide band LCR meter show it, but such things are a bit outside my budget. The nice Quadtech (IET) or Agilent ones are over $10k.

IMO again, if bypassing electrolytics has an effect, the correct design solution is really to bypass someplace else, either at the rectifiers to kill RF, or at the circuit where you're not fighting with the inductance of the wiring from the main caps. The correct return point for the bypass is also important, and it may not be where you think!
 
... IMO again, if bypassing electrolytics has an effect, the correct design solution is really to bypass someplace else, either at the rectifiers to kill RF, or at the circuit where you're not fighting with the inductance of the wiring from the main caps. The correct return point for the bypass is also important, and it may not be where you think!

Above 10KHz electrolytics behave differently, from brand to brand, from type to type. Wouldn't it be a explanation for differences in decoupling a ps?
 
Surely you realize that the filament is a resistor equal to whatever the other resistor's value is reduced by, to meet the biasing needs.

Not totally sure what you are saying here. Filament is usually one or two ohms added on to the cathode resistor - the DC filament supply goes through both the filament and the cathode resistor. The tube is biased at the voltage on top of the cathode resistor. This may be what you are saying? The total circuit is usually 5-50 ohms depending on the tube. I've been using filament bias for over a year on all input tubes. Resistor is 5 ohms on a 26 and 22.5 ohms on a 4P1L. I'm very happy with it.
 
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Not totally sure what you are saying here. Filament is usually one or two ohms added on to the cathode resistor - the DC filament supply goes through both the filament and the cathode resistor. The tube is biased at the voltage on top of the cathode resistor. This may be what you are saying? The total circuit is usually 5-50 ohms depending on the tube. I've been using filament bias for over a year on all input tubes. Resistor is 5 ohms on a 26 and 22.5 ohms on a 4P1L. I'm very happy with it.


1-2 ohms is when the filament is cold. Depending on the tube type, it rises to anywhere from 20 -80 ohms when the filament is hot.
 
You must excuse me but I have no idea what you are talking about. The last time I looked at ohms law 1.9v at 600mA was a resistance of 3.17 ohms. That's for a hot filament because unless I'm hallucinating, my amplifier is actually producing music.

I have no doubt your amp is singing beautifuly. It's just the filament biasing that is interesting. Using a filament for a bias resistor is uncommon. I've seen it a few times but not with the tubes you are using. Your DHT filament power and biasing circuit would be interesting. When you use the term "filament biasing," I'm taking that to mean you use the filament resistance to bias some other tube's cathode. I've seen it done with 12ax7 type tube heaters to bias output tubes and use their cathode voltage to power the 12ax7 heater. Is your scheme different?
 
Have a look at this:
 

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I thought the Coleman regulator board has an electrolytic cap (C15) from filament positive to ground?

Based on this version of Rod's (apologies if this is not representative of his latest/current design)
http://www.diyaudio.com/forums/tubes-valves/38248-new-dht-heater-4.html?postid=446973#post446973

Isn't that cap in effect acting like a cathode bypass?

It's exactly cathode bypass cap in his amp.

The regulator itself is not referenced to the ground at all. It connects between filament legs of the tube.
 
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